1. Field of the Invention
The present invention relates to a sheet punching device and an image forming apparatus having the sheet punching device for forming a punch hole in a sheet.
2. Description of the Related Art
In recent years, some image forming apparatuses such as cameras and laser beam printers have a sheet punching device, which punches a punch hole in a sheet on which an image is formed. A user files and uses the sheet in which the punch hole is formed by the sheet punching device.
In the sheet punching device, there is a case in which a burr is generated in the punch hole depending on a kind of sheet, a use environment such as temperature and humidity, and a time-dependent change such as abrasion. If the burr is generated in the punch hole of the sheet, when stacking the punched sheets to form a sheet bundle in a post process, burr portions of the stacked sheets overlap.
As a result, a stacking state of the sheets may be in disarray, or the burr of a next stacked sheet may be caught on the sheet bundle to cause misalignment of the stacked sheets. Thus, it causes a problem in post-processing the punched sheets.
For this reason, several punching devices, which do not generate the burr in the punched punch hole as little as possible, have been suggested. For example, a front end portion of a punch may have a sharpened configuration to prevent the burr from being generated when punching is performed by the punch as discussed in Japanese Patent Application Laid-Open No. 11-245198.
As a punching device, which punches a hole in a hard material to be processed other than a paper without generating the burr, there is discussed a device having the following configuration in Japanese Patent Application Laid-Open No. 2006-272496. As illustrated in FIG. 24, a punch hole is punched in a material for processing by a punch 40, which goes down, and a die hole 35a, which is formed in a die 35. A groove 41 is formed in an outer circumference of the punch 40, and a blade is formed even in a corner portion B12 located above the groove 41.
In the punching device, the punch 40 goes down in a Q direction, and punches a hole in the material to be processed by a blade A11 of the front end portion of the punch 40. Even when the burr is generated in the punch hole, the punch 40 further goes down in the Q direction to thereby remove the burr of the material to be processed by the corner portion B12 above the groove 41.
As described above, blades are formed in two portions of the punch 40, and when the punch 40 goes down, a punching operation is performed twice by the blades of the two portions and the die hole 35a. Therefore, generation of the burr at the time of punching the sheet is reduced.
However, in the conventional punching device for preventing the burr, it is difficult to sufficiently prevent the burr from being generated.
In the sheet punching device in which the front end portion of the punch is sharply configured, the burr may be generated when punching a sheet having low rigidity such as a thin paper or a sheet placed in the high-humidity environment.
The punching device illustrated in FIG. 24 can effectively remove the burr in a material to be processed, which is relatively hard such as a substrate. However, it is difficult to sufficiently remove the burr in a soft sheet such as a thin paper. It is due to the following reason. When punching the sheet by the front end portion A11 of the punch 40, the burr is generated on a surface of the sheet on the die 35 side. However, while the punch 40 is moving in the Q direction, the burr is pushed away by the front end portion A11 because the material is soft, and thus it is difficult to remove the burr.
As described above, since the burr cannot be sufficiently removed due to the material of the sheet to be punched or the use environment, there is a need for a sheet punching device that can certainly remove the burr.